QuantifyingMismatch in Solar Arrays

February 2013

2.2 MW InstallationTalmage Solar Engineering

Smart Modules Deliver:

• Arc, Fire and Safety Hazard Detection

• 30% Longer Strings, Lower BOS Costs

• Reduced Customer Acquisition Costs

• Increased Energy Harvest and System Uptime for Proven ROI

• Module-Level Monitoring, Reduced O&M and Commissioning Costs

• 25% More Power Density / Efficiency

Smart Modules Deliver:

• Arc, Fire and Safety Hazard Detection

• 30% Longer Strings, Lower BOS Costs

• Reduced Customer Acquisition Costs

• Increased Energy Harvest and System Uptime for Proven ROI

• Module-Level Monitoring, Reduced O&M and Commissioning Costs

• 25% More Power Density / Efficiency

Impedance Matching

Traditional Modules – String Current Defined by Weakest Module

Smart Modules – String Current Defined by Strongest Module

• Each Module Produces 100% of its Capacity

Strong Innovation• 50 Patents Submitted• 11 Patents Granted

The World’s First Certified Smart Module

• Junction box diodes replaced with intelligence

• The only product certified by TÜV for North America and Europe

• 3rd party validation

Mismatch in “Perfect” Arrays

• Voltage Variance of 15% on Perfectly Architected Array

• < 2-Years-Old Measured at Peak Production Time

Manufacturing Mismatch

Bin Power

Range

# of MFG’s

surveyed

3% total 2

5% total 3

6% total 3

10% total 2

Mean 5.9% range

Median 5.5% range

• Crystalline structures have inherent differences

• No two solar cells are ever identical

• Typical binning range is over 5%

• Flash testing accuracy broadens range

Variable Degradation

• Module degradation is not uniform

• Approximately 0.75% increase in standard deviation each year

• Data published by NREL shows differences in degradation speeds across modules

• In year 5, this represents 1-2% additional losses, which grow to ~4% in year 10 and 12% in year 20

Source: “Outdoor PV Degradation Comparison”. D.C. Jordan, R.M. Smith, C.R. Osterwald, E. Gelak, and S.R. Kurtz. NREL Conference Paper CP-5200-47704

PV Evolution Labs

Tigo Energy Analysis

Mismatch from Clouds

• NREL Oahu dataset:

– 17 lightmeters at one location

– 1-second intervals

– 1 full year of data

• 15.4% average standard deviation¹ in irradiance due to clouds

• Corresponds to 5-8% in lost energy due to mismatch

Note¹: Weighted by power production at each second; excluding lightmeter readings lower than 75W/m²

Source: Tigo Energy analysis

0%

5%

10%

15%

20%

25%

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly Standard Deviation

Uneven Soiling

• Driven by various factors:

• Level of dust in the air

• Proximity to roads

• Proximity to birds and plants

• Long term variance leads to hotspot

• Reduced efficiency = increased resistive losses = further reduction of efficiency

• Estimated mismatch losses: 1-4%

Thermal Mismatch

• Measured thermal mismatch on flat commercial rooftops in Northern California:

– Average of 4-7 C range between max & min

– Corresponds to 2-4% mismatch in module power output

– Maximum of 20 C spread

• First Solar said they have module operating temperatures differ by 10 C or more¹ in ground-mount arrays

Source¹: “PV Performance Modeling Workshop Summary Report”; Cameron, Stein, and Tasca; Sandia National Labs; May 2011

Source: Tigo Energy analysis

68 71 71 72 72 74 75 73 73 70 71 72 68

69 67 74 77 79 78 77 78 78 75 70 70 71

72 71 74 76 79 85 81 82 75 77 73 73 70

67 68 74 77 78 79 77 75 77 80 74 69 68

65 68 71 71 74 75 72 72 74 72 72 72 67

Module Temperatures on a Rectangular Array

Failed Bypass Diodes

• 0.5% of modules have failed bypass

diodes on day one.

• Results in 0.5% system power loss

• Difficult to detect with typical

measuring devices

Accumulated Wear and Tear

• 9 year old retrofit

• 25% improvement in performance when optimized – more when modules were replaced

• 10 modules (3.0% of system): producing 90% of peers

• 12 modules (3.6% of system): producing 50% of peers

• 76 modules (22.7% of system): producing 20% of peers

• Two strings (7.2% of system): open-circuit fault

Mismatch Summary

Module binning mismatch 3.0%

Thermal mismatch 1.0%

Variable soiling 0.5%

Cloud variance 1.0%

% failed diodes found 0.5%

Variable degradation (per year) 0.5%

Total Mismatch (Year 1) 5-7%

Total Mismatch (Year 5) 7-9%

Total Mismatch (Year 15) 12-15%

Standard Deviation Range from 1 to 25%+

In Tigo Energy’s installations, average standard deviation of 11.3%

ASU-APS (STAR) Test Results

Source: Dr. Mani, PV Power Plants Conference, 12/2011

• 1900 modules cleaned prior to inspection

• 10-17 years in the field

• Annual degradation range 0.93 – 1.92%

• Modules sold at ~$4/W

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

10.7 12.3 17

Weakest

Strongest

Degradation Comparison (Strong vs. Weak)

Thank You!

Evan Sarkisian

Tigo Energy